JPS622109B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for regenerating degraded bentonite mud water discharged from foundation holes during civil engineering foundation work and having impurities such as sand and gravel mixed into the bentonite solution.
The purpose of this is to efficiently remove gravel and earth and sand impurities with large particle sizes and high specific gravity from degraded bentonite muddy water containing impurities such as gravel and cement, and to convert the degraded bentonite muddy water to a specific gravity and viscosity suitable for protecting foundation holes. An object of the present invention is to provide a method for regenerating degraded bentonite mud that can be regenerated into a bentonite solution. Conventionally, in order to protect the walls of the foundation hole, a bentonite solution is injected into the foundation hole, and then concrete is flowed into the foundation hole from the bottom of the foundation hole using a Doremi pipe, and the bentonite solution and concrete are mixed. There is a construction method in which bentonite solution is discharged from the foundation hole based on the difference in specific gravity, and concrete piles or underground continuous walls are driven into the foundation hole. In this conventional construction method, the bentonite solution discharged from the foundation hole becomes degraded bentonite slurry containing impurities such as sand and gravel, and if this degraded bentonite mud is reused as it is to protect the walls of other foundation holes The function of protecting the hole wall cannot be achieved sufficiently, and furthermore, when concrete is poured into the foundation hole, the degraded bentonite mud and the concrete for foundation pile driving mix, resulting in a significant decrease in the strength of the concrete pile. There was a problem. Therefore, such degraded bentonite mud was normally discarded, but because this degraded bentonite mud is strongly alkaline, it cannot be dumped into the ocean at all, and its disposal is difficult, and the bentonite solution itself is expensive. Therefore, there was a problem in that the cost would be high if it was discarded every time it deteriorated. In view of the above circumstances, the inventors continued intensive research on the mechanism of action of the bentonite solution itself, and as a result, they found that the viscosity of the bentonite solution used to protect the walls of the foundation hole was 20 to 22 (seconds/500c.c.). It was discovered that when the specific gravity is set to 1.04 to 1.10, the difference between the viscosity and specific gravity of concrete is large and the miscibility with concrete decreases. They have repeatedly found that this can be obtained when the concentration of the bentonite solution is 7 to 8%. In addition, as a result of intensive research on degraded bentonite mud containing impurities such as gravel and cement, the inventors found that the particle size of solid impurities such as gravel contained in degraded bentonite mud was 10μ or more. They discovered that the viscosity and specific gravity of degraded bentonite mud increases, causing it to mix with concrete. Based on these findings, the inventors removed solid impurities with a particle size of 10 μm or more from degraded bentonite mud and regenerated a bentonite solution with desired characteristic values that is mainly composed of montmorillonite components with a particle size of 10 μm or less. He continued his research. On the other hand, there is a known method for recycling degraded bentonite mud using a cyclone for civil engineering work, as shown in Japanese Patent Publication No. 53-22047. When the above-mentioned separation work was carried out, it was found that if the discharge speed of the degraded bentonite slurry discharged into the cyclone was slow, impurities such as sand and gravel could not be sufficiently separated, whereas when the discharge speed was increased, the once separated sand and gravel It was also discovered that the existing method disclosed in the above-mentioned publication could only remove solid matter such as sand with a size of about 74 microns or more, as it was disturbed by the strong muddy water. In addition, the inventors found that by applying a multi-stage multi-cyclone used in fine chemistry rather than for civil engineering work, it was possible to separate solids with a particle size of 10μ or less and solids with a particle size of 10μ or more. However, with this multi-cyclone, it is necessary to reduce the diameter of the cyclone in order to increase the inflow velocity of the material to be separated. When treating degraded bentonite muddy water that contains bulky shells, etc., coarse sand and gravel or shells get stuck inside the cyclone, making the cyclone itself unusable.In the end, the multi-cyclone method is not suitable for processing rough objects such as civil engineering work. It was also determined that it was not suitable for use. Therefore, as a result of further intensive research, this inventor used a specific vertical centrifugal sedimentation machine as a separator without using a polymer flocculant, and developed a rotating drum built into this specific vertical centrifugal sedimentation machine. By rotating and applying a specific centrifugal force to the degraded bentonite mud, we succeeded in removing impurities consisting of solid particles such as gravel and cement with a particle size of 10μ or more from the degraded bentonite mud, which led us to create this invention. It's ivy. An embodiment of this invention method will be described in detail below based on the drawings. FIG. 1 is a process diagram showing one embodiment of the method of this invention, and 1 is a foundation hole excavated by a foundation excavation machine (not shown), and inside this foundation hole 1 there is a hole wall 1.
A bentonite solution 2a is injected to protect the base hole 1 and prevent collapse of the foundation hole 1. Insert the reinforcing bars 3 and Doremi pipe 4 into this foundation hole 1,
When concrete is poured into the bottom of the foundation hole 1 from the concrete mixer truck 5 through this Doremi pipe 4, bentonite solution 2, which has a specific gravity lighter than concrete, is poured into the bottom of the foundation hole 1.
a is pushed up by the concrete, and is passed through the pipe 24a by the suction pump 6 to the foundation hole 1.
is discharged from. The bentonite solution 2a discharged here contains impurities 25 such as sand and gravel coming out from the hole wall 1a, and these impurities 25 affect the specific gravity, viscosity, etc.
It is a degraded bentonite muddy water 2b with a high pH value. If the discharged degraded bentonite mud 2b contains coarse gravel, etc., as shown in FIG. It is desirable to remove coarse gravel and the like in advance using the sorting device 26. Next, the neutralizing agent stored in the neutralizing agent storage tank 8 is added to the degraded bentonite muddy water 2b poured into the muddy water storage tank 7 by opening the valve 9, and the degraded bentonite muddy water 2b is adjusted to an appropriate pH value of 7 to 10. lower to a value. Degraded bentonite mud water 2 in an embodiment of this invention method
The purpose of neutralizing b is that when the degraded bentonite muddy water 2b is separated into the bentonite solution 2a and the impurity 25, each of the bentonite solution 2a and the impurity 25 is not strongly alkaline but neutral, and the bentonite solution 2a is reused. This is to facilitate the use and disposal of impurities 25. Here, as the neutralizing agent, mineral acids such as hydrochloric acid and sulfuric acid, ferric chloride, sulfuric acid, and the like are preferably used. In addition, in this illustrated embodiment of the invention method, the aeration device 10 is operated as shown in FIG.
is opened and the air is guided to the muddy water storage tank 7 in which the degraded bentonite muddy water 2b has been accumulated for aeration, and the degraded bentonite muddy water 2b and the neutralizing agent are sufficiently mixed to complete the neutralization reaction and reduce the viscosity of the degraded bentonite muddy water 2b. This prevents unevenness. The degraded bentonite muddy water 2b neutralized in the muddy water storage tank 7 in this manner is guided by the pump 11 to the vertical centrifugal sedimentation machine 12 through the pipe 24b, as shown in FIG. Here, there are centrifugal sedimentators with rotary blades, such as so-called separator plate type centrifugal sedimentators and decanters, but when these are used, sand and gravel collide with the rotor blades, causing the rotor blades to become damaged. Because they wear out and break, they often need to be replaced, resulting in extremely poor workability. Therefore, in the method of this invention, as shown in FIG. 2, the rotating shaft 28 is inserted into the cylinder from the center of its upper surface, the solution outlet 27 is provided on the side wall of the bottom, and the impurity 25 is discharged from the center of the bottom. Exit 29
A bottom plate 33 having a cylindrical shape and having an inwardly bent weir 23 formed at the upper part and longer than the weir 23 and bent inwardly at the bottom part.
A vertical centrifugal centrifuge is constructed of a rotating drum 21 provided with a rotating drum 21, which is installed inside the box 32 with a required gap from the inner wall 32a of the box 32, and which is connected to a rotating shaft 28. A settler 12 is used. The degraded bentonite slurry 2b led to the vertical centrifugal sedimentator 12 through the pipe 24b
The slurry is fed into the vicinity of the bottom side wall of the rotary drum 21 installed in the vertical centrifugal sedimentator 12 through the slurry supply port 20 of b. Centrifugal force is applied to this fed degraded bentonite muddy water 2b by the rotation of the rotating drum 21,
As shown in FIG. 2, impurities 25 such as sand and gravel with large particle sizes and high specific gravity are accumulated on the peripheral wall 22 of the rotating drum 21, while bentonite solution 2a containing montmorillonite components with small particle sizes overflows the weir 23. , the solution outlet 2 is guided to the bottom of the box 32 through the gap between the rotating drum 21 and the inner wall 32a of the box 32, and is provided at the bottom of the box 32.
7 to the outside of the vertical centrifugal sedimentation machine 12. Here, the rotating drum 21 of the vertical type centrifugal sedimentation machine 12
If the centrifugal force due to the rotation of the rotating drum 21 is less than 100 G, the impurities 25 such as gravel and cement, which have slightly smaller particle sizes, cannot be removed sufficiently.
At 1000G or more, even the montmorillonite component in the degraded bentonite mud 2b is removed, so in the method of this invention, it is desirable to select a rotation speed such that the centrifugal force applied to the degraded bentonite mud is 100 to 1000G. In the method of this invention, in order to efficiently separate impurities, it is more desirable to select a rotational speed such that the centrifugal force is 240 to 440 G. In this way, the impurity 25 is separated and the discharge port 2
Bentonite solution 2a discharged from 7 is sent to regeneration tank 18 through pipe 24c. Bentonite solution 2a sent into regeneration tank 18
Then, a new high-concentration bentonite solution 2a is injected from the bentonite solution storage tank 17, or bentonite powder is added thereto, and the concentration of the bentonite solution 2a is adjusted in the regeneration tank 18. In this illustrated embodiment, as shown in FIG. 1, the air from the aeration device 10 is sent into the regeneration tank 18 by opening the adjustment valve 10b to aerate and mix the bentonite solution 2a, thereby making the concentration of the bentonite solution 2a uniform. It's on. Bentonite solution regenerated in this way 2
A is fed into a foundation hole 1 different from the foundation hole 1 described above by the pump 19, and is used to protect the hole wall 1a of the foundation hole 1. On the other hand, the rotating drum 21 of the vertical centrifugal sedimentation machine 12
The impurities 25 consisting of solid matter with a particle size of 10μ or more accumulated on the peripheral wall 22 are removed by eccentrically attaching a scraping blade (not shown) to the rotating shaft 28 of the vertical centrifugal sedimentator 12 after stopping the feeding of the degraded bentonite slurry 2b. attachment,
This scraping blade (not shown) scrapes impurities 25 from the peripheral wall 22 of the rotating drum 21, discharges them from the discharge port 29 at the bottom of the vertical centrifugal sedimentator 12, and loads them onto the truck 31 using a belt conveyor 30 or the like. Release with. The method for regenerating degraded bentonite mud according to the present invention having such a configuration involves injecting degraded bentonite mud discharged from the foundation hole and containing impurities such as gravel and cement into a rotating drum installed in a vertical centrifugal settler. , rotate this rotating drum
A centrifugal force of 100 to 1000 G is used to remove impurities such as sand and gravel of 10μ or more from degraded bentonite mud to regenerate a bentonite solution, and a highly concentrated new bentonite solution or bentonite powder is added to the regenerated bentonite solution. Since the bentonite solution is adjusted to a concentration suitable for protecting the walls of the hole, impurities such as gravel and earth that could not be separated with conventional cyclones for civil engineering work can be removed using the rotating drum of the vertical centrifugal sedimentation machine. It can be easily removed by adjusting the rotation speed, and impurities of 10μ or larger can be easily and reliably removed without clogging unlike the multi-stage multi-cyclones used in fine chemistry. This is a method for regenerating degraded bentonite mud that has excellent effects. Finally, Table 1 shows a comparison of the viscosity, specific gravity, and sand fraction (100 x sand/bentonite solution) of the bentonite solution regenerated by the method of this invention with that of the degraded bentonite slurry before the regeneration treatment. , to make the effects of this invention even clearer.

[Table] As shown in this table, the bentonite solution regenerated by the method of this invention has a very low sand fraction of 2 to 4%, has very little impurity with large particle size, and has a high viscosity. is 20 to 22 (seconds/
500 c.c.), and the specific gravity was 1.04 to 1.10, which is approximately the same value as a bentonite solution with a concentration of 7 to 8%, and the difference between the viscosity and specific gravity of concrete was large. Also, judging from these viscosity (sec/500c.c.) values, specific gravity, and sand fraction, it is inferred that only solid components with a particle size of 10 μm or less remain separated. As is clear from these results, the method for regenerating degraded bentonite mud according to the present invention can easily and reliably remove impurities such as gravel from degraded bentonite mud, and can be used to protect the walls of foundation holes. It can be regenerated into a suitable bentonite solution, and the regenerated bentonite solution has a much lower viscosity and specific gravity than concrete, so even when it is injected into the foundation hole again and concrete is poured, the bentonite solution and concrete do not mix. It is understood that the concrete is not mixed together, the concrete can be placed sufficiently, and the strength of the placed concrete is also high.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an example of this invention method;
FIG. 2 is a schematic cross-sectional view of the centrifugal sedimentation machine used in the same example. 1... Foundation hole, 1a... Hole wall, 2a... Bentonite solution, 2b... Degraded bentonite mud, 1
2... Vertical centrifugal sedimentation machine, 21... Rotating drum,
23...Drain, 25...Impurity, 27...Solution outlet, 28...Rotary shaft, 32...Box, 33
……Bottom plate.

Claims (1)

[Claims] 1. The process of lifting degraded bentonite mud water containing impurities such as sand and gravel into the bentonite solution from the foundation hole, and a cylindrical shape with a rotating shaft inserted from the center of its top surface and a solution outlet at the bottom. Inside the box, a rotating drum having a cylindrical shape and having an inwardly bent weir formed at the top and an inwardly bent bottom plate longer than the weir at the bottom is connected to the rotating shaft. Using a vertical centrifugal sedimentation machine which is installed inside the box with a required gap between the inner wall of the box and the box, the lifted degraded bentonite slurry is injected into the vicinity of the lower side wall of the rotary drum of the vertical centrifugal sedimentation machine, and then rotated. A step of rotating a drum to apply a centrifugal force of 100 to 1000 G to the degraded bentonite mud to remove impurities such as gravel and earth from the degraded bentonite mud to regenerate a bentonite solution, and to adjust the regenerated bentonite solution to the required concentration. A method for regenerating degraded bentonite mud, comprising: